Simulation and analysis of single fiber pull-out tests through ANSYS and VC++

The aim of this study was to simulate the traditional investigation process of single fiber pull-out tests on quantificational basis, with an estimation of the critical length of embedded fiber and interfacial shear strength while comparing the stimulation results with empirical results. A finite element method (FEM) model of single fiber pull-out tests was established by using ANSYS parametric design language (APDL) program flow. Interfacial average shear strength was calculated and process of interfacial debonding was simulated. Single fiber pull-out tests were implemented to validate the FEM model. Results reveal that the maximum load estimated by the FEM varied as a function of both the length and critical length of the embedded fiber, and the calculated interfacial shear strength through FEM analysis is basically in agreement with the experimental results with a trivial difference of no more than 4.5%. A software was designed to simplify the simulation with respect to the analysis system of single fiber pull-out tests.     

Friction and wear behavior of aluminum-graphite composites as a function of interface and fiber direction

The friction and wear behavior of aluminum-graphite fiber composites was examined as a function of the interfacial reaction zone. Sliding wear tests were performed on three different fiber orientations on a standard pin-on-disk tribology machine. The counterface was made of gray cast iron with a surface hardness of 92 HRB. The wear rate and friction coefficient were found to decrease exponentially with sliding time and eventually reached a steady state condition. This was attributed to the development of a lubricating transfer film on the sliding surface. The wear mechanism was investigated through the use of scanning electron microscopy analysis. A wear model was developed for specimens worn with fibers parallel to the sliding direction. This model incorporates three dominant wear mechanisms: (1) matrix removal by delamination, (2) fiber wear due to plowing and (3) fiber pull-out. The model was evaluated numerically and was found to agree with the experimental data. The model predicts that whenever fiber pull-out is a contributing mechanism in the wear, the wear rate is an exponential function of the normal load. In contrast, the wear rate of composites is proportional to the normal load in the absence of fiber pull-out.     

Effect of the yarn pull-out velocity of shear thickening fluid-impregnated Kevlar fabric on the coefficient of friction

This study explains the yarn pull-out process behavior of woven fabrics in relation to their mechanical properties. Empirical research on the relationship between the yarn pull-out behavior and fabric properties are evaluated, along with a detailed comparison of friction between the fabric fibers in static and dynamic modes. Samples are tested in three modes, namely, neat, dissolved liquid, and silica particle- based Shear thickening fluid (STF)-treated fabric. Accordingly, the presence of STF increases friction between the fabrics and the warp and weft yarns, as well as prevents the displacement of the yarns. Increased friction also leads to an increase in the energy absorption of the yarn pull-out process. In this research, the pull-out test has been performed at three different velocities: 50, 250 and 500 mm/min. Results show that increases in the pull-out velocity increase the pull-out force of the neat and dissolved liquid samples. By contrast, the behavior is completely opposite in the STF-treated sample. Comparing the yarn pull-out values indicates that the STF-treated samples have the highest value, which is approximately three times higher than that of the neat sample.     

Tribological Characteristics of Sustainable Fiber-Reinforced Thermoplastic Composites under Wet Adhesive Wear

The friction and specific wear rate of sustainable kenaf fiber–reinforced polyurethane composites were investigated against stainless steel counterface and under wet contact conditions. The new composites were evaluated at different applied loads (50–80 N), sliding distances (up to 2.7 km), and fiber mat orientations. Scanning electron microscopy (SEM) was used to observe the damage features on the worn surfaces. The results revealed that sustainable kenaf fibers assisted in enhancing the wear and frictional performance of the polyurethane thermoplastic composite by about 59 and 90%, respectively. Operating parameters and mat orientation controlled the wear and the frictional behavior of the composite. Better wear performance was exhibited at high loads and when the fiber mats were oriented perpendicularly to the sliding direction. Observations of the worn surfaces revealed different features of damage such as microcracks, fiber tearing, fiber detachment, and delamination. However, there was no trace of fiber pull-out in any of the tested conditions.     

Experimental study on pullout performance of sensing optical fibers in compacted sand

The distributed optical fiber sensing systems have played an increasingly important role in monitoring civil infrastructures over the past few years. One of the main challenges of their applications to geotechnical monitoring is to increase the reliability of strain sensing optical fibers in measuring the deformation of surrounding soil masses. In this paper, a pullout test method is proposed to characterize the deformation compatibility between an optical fiber and soil. A series of pullout tests on three types of sand-embedded optical fibers are conducted to investigate the performance of the fiber–sand interface. Based on the test results, an explicit tri-linear pullout force–displacement relationship is proposed to describe the mechanical behavior of the fiber–sand interface. The performance of the three fibers regarding fiber–sand interaction mechanism is evaluated in terms of ratio of effective pullout displacement to diameter, ratio of residual pullout displacement to diameter, peak shear strength and residual shear strength. All four parameters of the three fibers are found to have approximately linear relationships with the applied confining pressure, which reveals that the deformation compatibility of the fiber–sand interface is utterly dependent on the confining pressure. For all the three fibers, the first shear stiffness coefficient is about 8 N/mm and the ratio of residual to peak shear strength is about 0.5. Furthermore, the Mohr–Coulomb failure criterion is used to get the cohesions and friction angles of the three fiber–sand interfaces. Through a comparison of the pullout performance, one out of three types of fibers tested is found to be more preferable for soil deformation measurement in laboratory-scale tests. The conclusions can provide valuable references for predicting the fiber–soil interface behavior and evaluating the reliability of strain monitoring data.     

A dynamic asymmetrical crack model of bridging fiber pull-out in unidirectional composite materials

As a rule, when a crack happens in composite materials, the fibrous system will generate bridging fibers resulted in the asymmetrical extending of the crack. In this paper, a dynamic asymmetrical crack model of bridging fiber pull-out in unidirectional composite materials is built for analyzing the distributions stress and displacement with the internal asymmetrical crack under the loading conditions of an applied non-stress and the traction forces on crack faces yielded by the bridging fiber pull-out model. Thus the fiber failure is determined by the maximum tensile stress, the fiber ruptures, and hence the crack propagation should also occur in self-similar modality. The formulation involves the development of a Riemann-Hilbert problem. The analytical solution of an asymmetrical extension crack in unidirectional composite materials under the conditions of moving increasing loads Pt²/x² and Px²/t is concluded, respectively. Based on relative material properties, the variable law of dynamic stress intensity factors was depicted perfectly. After the conclusion of analytical solutions with the superposition theorem, the solutions of arbitrary complex problems could be acquired.     

Interfacial Properties of Carbon–Rubber Interfaces Investigated via Indentation Pull-Out Tests and the JKR Theory

Properties of the interface between the filler and the matrix of a composite material draw research attention due to their contributions to the overall properties of the material, especially when the filler and the matrix differ significantly from each other. The work reported in this paper investigates the interface between amorphous carbon and a cross-linked synthetic natural rubber. The interface was experimentally simulated with the surfaces of a sputtering-coated carbon on a spherical Al₂O₃ tip and a flat synthetic natural rubber sample. Step-loading and pull-out tests with a micro-/nano-indentation instrument were conducted. Fully relaxation of the samples occurred during both test procedures. The penetration depth, applied load, and experimental time were recorded during each test. The Johnson–Kendall–Roberts theory was used to analyze the data at the initial point (step-loading) and the final surface separation point (pull-out) to obtain the initial equivalent modulus, infinite equivalent modulus, work of adhesion, and the average normal interfacial strength at separation. It is found that the pull-out force and the work of adhesion depend on the unloading rate, but the infinite equivalent modulus and the average interfacial strength in the normal direction of the carbon–rubber interfaces are independent of the unloading rate in current experimental domain.     

碳纤维增强树脂基复合材料切削机理研究

碳纤维增强树脂基复合材料（Carbon fiber reinforced plastic,CFRP）在细观尺度上由纤维、树脂及界面不同相组成,在宏观尺度上呈层叠特征,具有非均质性和各向异性。CFRP切削过程的实质是在切削力、热共同作用下同时去除高强度纤维和低强度树脂的复杂过程,极易出现加工损伤。抑制加工损伤的前提是准确揭示CFRP切削机理,而揭示其切削机理的关键是分析材料去除过程。由于纤维是复合材料内部承受主要载荷的组成相,材料的去除过程主要由纤维的断裂过程决定。因此,通过分析切削过程中纤维的受力状态,以双参数弹性地基梁理论为基础,建立了虑及纤维所受法向及切向约束,且兼虑树脂及界面温变特性的单纤维切削模型,可准确表征纤维实际受力状态,实现纤维断裂过程的准确求解。研究发现：切削深度和纤维角度影响纤维变形深度,即切深越大,纤维变形深度越大,更易产生加工损伤;随着纤维角度增加,纤维变形深度减小。同时,为解决单纤维切削模型难以直接验证的难题,利用其求解得到宏观切削力理论值,通过与试验值对比,间接验证了单纤维切削模型的正确性。同时与未考虑被切削纤维所受切向约束和树脂及界面温变特性时相比,同时考虑这两个因素可使CFRP宏观切削力计算精度平均提升20%。所建立的单纤维切削模型不仅能够从细观尺度准确揭示CFRP去除机理,而且可为后续有关损伤抑制的研究提供理论依据。     

Tribological properties of short glass fiber reinforced polyamide 12 sliding on medium carbon steel

The friction and wear of short glass fiber reinforced polyamide 12 (PA12) were investigated. The behavior of the fibers on a sliding surface and their effect on the friction and wear were studied in terms of the amount and orientation of the fibers in the composite. Results showed that the friction level and wear resistance were strongly affected by the fiber content, and glass fiber patches produced on the sliding surface played important roles in the wear resistance of the composite. The optimum fiber content for the best wear resistance of the PA12 composite was approximately 30 wt.% and higher fiber contents had no added effect on the wear amount. The applied load also strongly affected the wear resistance due to the increase in temperature at the sliding interface, and an increase in rapid wear was observed when the interface temperature increased above the glass transition temperature of PA12. On the other hand, the fiber orientation had less effect on the friction and wear of the composite compared to the fiber content and applied load. Based on the behavior of glass fibers on the sliding surface and wear debris analysis, the wear mechanism of the PA12 composite is discussed.     

3D打印连续纤维复合材料丝材的成形规律

针对3D打印连续纤维增强热塑性树脂复合材料,研究了热塑性树脂在螺杆挤出过程中的流动机理和在纤维界面的浸渍行为,揭示了螺杆转速和牵引速度对复合丝材成形直径和纤维含量的影响规律。提出使用实际浸渍时间和理论完全浸渍时间来共同表征树脂对纤维的浸渍程度,观察复合丝材断面的形貌可知,高浸渍程度的丝材内部空隙较少,树脂和纤维结合更紧密。进行3D打印成形测试,当丝材的浸渍程度从17.25%提高到40.02%,样件的拉伸强度可从132 MPa提高到160 MPa,提高约21%。对样件进行动态力学性能分析(DMA)测试,试验结果表明浸渍程度高的复合材料成形件具有高的存储模量和损耗模量,表明其纤维和基体间的界面结合程度得到了提高和改善。     

碳纤维增强复合材料水导激光切割试验研究

采用正交试验方法对影响水导激光切割碳纤维增强复合材料（CFRP）的关键工艺参数进行了深入研究,得出了进给速度、水射流速度、脉冲频率和激光功率对切割CFRP的影响规律,并用直接对比法和极差分析法所得最优参数进行单次划槽切割对比。研究结果表明：在极差分析法所得最优参数下切割CFRP时,切缝深度增大3.2%、切缝宽度减小9.2%、切缝锥度减小11.8%、线粗糙度减小40.2%。通过与干式激光加工方法对比发现,水导激光加工技术在切割CFRP方面优势明显,由于水射流的冲刷和冷却作用,材料切割表面几乎无热影响区和纤维拔出。另外,采用正交试验所得最优工艺参数实现了4 mm厚度CFRP的无锥度切割。     

基于SCM的光纤预制棒气相沉积机床控制系统

在了解光纤预制棒加工工艺的基础上,选择MCVD法为研究对象.考虑到光纤气相沉积技术要求控制系统高度自动化和可靠性,研制了以单片机为处理芯片的控制系统,设计了包括微处理器模块、过程通道模块、人机接口模块等硬件组成以及控制系统软件的实现方法.实现了性能合格的光纤预制棒产品的生产.     

芳纶纱的结构形貌对芳纶/PTFE织物复合材料摩擦学性能的影响

为了研究纱线结构形貌对织物复合材料摩擦学性能的影响,选用对位芳纶纤维,制备成3种具有不同结构形貌的芳纶纱,分别为长丝平行纱、长丝加捻纱和短纤维加捻纱。以相同的制备工艺得到3种芳纶/PTFE织物复合材料,采用多试件摩擦磨损试验机测试复合材料的摩擦学性能,并对芳纶/PTFE混编织物及相应复合材料的结构形貌、力学性能和磨损表面进行分析与探讨。实验结果表明：芳纶纱的结构形貌可直接影响纱线的断裂强度、纱线拔出强力、纱线与树脂的界面结合力,进而影响织物复合材料的摩擦学性能;在不同的磨损条件下3种混编织物的耐磨性表现有所不同,当载荷相对较低时,芳纶短纤维加捻纱/PTFE织物复合材料磨损率更低,而当载荷较高时,芳纶长丝加捻纱/PTFE织物复合材料耐磨性更好。     

Plastic deformation behavior of a uniaxial metal matrix composite under transverse compression

Plastic deformation behavior of a stainless-steel/Sn−Bi composite was examined using transverse compression tests on rectangular specimens under plane strain loadings. Based on the anisotropic yield criterion proposed by Hill, a theoretical analysis on the relationship between the yield strength of the matrix material and the yield strength of the composite was developed and compared to experimental results. Experiments were carried out to investigate the effects of the forming parameters such as yield strength of the matrix material, fiber packing patterns, fiber volume fraction, and lubrication of the compression platens, on the plastic deformation behavior of the metal matrix composite. Failure modes of the composite included shear band formation and eye formation at the fiber-matrix interface. Low deformability in the transverse directions was found for the metal matrix composite specimen. The theoretical and experimental results on the effects of the forming parameters provide basic information for further research on the transverse compression of metal matrix composite materials.     

贝壳的力学性能和增韧机制

对具有交错纹片结构的黄米螺壳进行压缩和三点弯曲实验.实验结果表明贝壳的力学性能与其显微结构密切相关,且存在各向异性.压缩和弯曲实验的结果表明,垂直于层面方向的承载能力均高于垂直于横截面方向的承载能力;当贝壳中的有机质被去除后,其三点弯曲强度只有原来的1/20～1/30.贝壳材料主要增韧机制为裂纹偏转和纤维拔出以及有机质的粘弹性作用.对贝壳材料增韧机制的仿生研究为复合材料的设计提供有益信息.     

纤维金属层板铆接剩余强度影响因素研究

为研究单搭铆接接头中纤维金属层板耦合损伤行为,运用金属硬化Johnson-Cook失效准则、纤维增强复合材料三维Hashin损伤准则、脱层B-K失效理论以及刚度退化失效准则建立了纤维金属层板铆接渐进失效模型,并结合实验验证了模型的合理性。考察了单搭铆接二次弯曲效应、层板铝合金体积分数、预紧力、层板孔边距对纤维金属层板铆接强度和失效模式的影响,为提高纤维金属层板铆接剩余强度提供可靠建议。分析结果表明：二次弯曲效应加速损伤发生,从而降低层板铆接强度,其中偏心加载可以削弱二次弯曲效应,更好地提高铆接强度;层板铝合金体积分数的增大能够提高层板铆接强度,但当体积分数大于50%时层板铆接比刚度和比强度反而下降;预紧力的增加能够提高层板铆接强度和增强层板损伤抗力;随着孔边距的递增,铆接剩余强度有所提高,破坏模式由灾难性拉断失效模式逐渐转化为理想的挤压失效模式,但当孔边距达到一定数值时,铆接强度不再明显提高,而失效模式也维持为挤压破坏。     

EFFECT OF MICROWAVE TREATMENT ON WC INSERTS FOR DRILLING OF GFRP COMPOSITES

Due to excellent properties such as high specific strength, high specific modulus, and corrosion resistance, Glass Fiber Reinforced Plastics (GFRP) find wide applications particularly in the aerospace and automotive industries. In order to fabricate structural components of GFRP to near-nett shape, machining of GFRP composites is necessary. Drilling is the most common machining operation for GFRP composites. The fiber pull-out, cracking of matrix during the entry and exit of drill, rapid tool wear, and hole shrinkage are problems associated with machining of GFRP. The present study attempts an innovative idea of improving the cutting performance of Tungsten carbide (WC) inserts (K-20) by post-sintering using microwave irradiation.     

芳纶表面处理对纤维增强橡胶基复合密封材料性能的影响

采用横向抗拉强度作为表征芳纶纤维增强橡胶基密封材料中纤维与橡胶粘结强度的指标,通过材料横向拉伸试样断口的形貌分析,探讨了不同的粘合体系和纤维表面处理工艺对芳纶纤维与橡胶结合度的影响。结果表明：用RFL乳液处理过的芳纶纤维增强橡胶基复合密封材料的性能最佳。     

C/SiC复合材料组织对磨削力与加工表面质量的影响

采用树脂结合剂金刚石砂轮对C/SiC复合材料与SiC陶瓷进行了平面磨削加工试验,通过对比两种材料的磨削力及磨削加工表面质量,分析了C/SiC复合材料组织与其磨削加工特性的 关系。研究结果表明,C/SiC复合材料中碳纤维及SiC基体皆以脆性断裂方式实现材料去除;与SiC陶瓷的加工表面(其表面粗糙度值Ra为0.2~0.3μm)相比,C/SiC复合材料磨削时由于碳纤维层状断裂、拔出及其与SiC非同步去除现象导致其加工表面粗糙度值较高, Ra为0.8~1.0μm;C/SiC复合材料磨削力较小,是相同工艺参数下SiC陶瓷材料磨削力的35%~76%。     

固化方式和纤维表面处理对碳纤维-树脂界面化学组成的影响

对碳纤维进行低温等离子法表面处理,分别在室温和微波固化条件下将碳纤维与环氧树脂复合成型,制备出碳纤维复合材料.采用原子力显微镜、拉曼光谱对碳纤维表面形貌和微观结构进行表征,采用扫描电镜和能量散射光谱对碳纤维-树脂界面区形貌和元素分布进行表征.结果表明,碳纤维经处理后,表面无序结构比例增大,有利于提高纤维的微波吸收能力,使微波固化复合材料的界面结合比室温固化复合材料更牢固.经过表面处理的碳纤维与树脂形成良好的化学键合,S i元素在复合材料界面区发生偏聚.